If the patient is an inpatient, the patient's nurse will administer the doses as per hospital drug administration policy, subcutaneously at 8:00 am and 8:00 pm. Immediately prior to receiving her fourth dose, an anti-factor Xa level will be drawn - called the "pre-dose" level. Waiting until this time period allows enoxaparin to reach adequate steady-state levels based on an average elimination half-life of 4.5 hours (range 3 to 6 hours). Three hours after the fourth dose of enoxaparin is administered, another anti-factor Xa level will be drawn - called the "3-hour post-dose" level. Eight hours after the fourth dose of enoxaparin is administered, an anti-factor Xa level will be drawn as well - called the "8-hour post-dose" level. The same set of levels will be measured during admission after any dosage adjustments. Enoxaparin dosage changes will be made at the discretion of the treating physician.